The original sense was of motion, which led to that of lifting, then to that of "measure the weight of." The older sense of "lift, carry" survives in the nautical phrase weigh anchor. Figurative sense of "to consider, ponder" (in reference to words, etc.) is recorded from mid-14c. To weigh in in the literal sense is from 1868, originally of jockeys; figurative meaning "bring one's influence to bear" is from 1909.
Old English gewiht "weighing, weight, downward force of a body, heaviness," from Proto-Germanic *wihti- (source also of Old Norse vætt, Danish vegt, Old Frisian wicht, Middle Dutch gewicht, German Gewicht), from *weg- (see weigh).
Figurative sense of "burden" is late 14c. To lose weight "get thinner" is recorded from 1961. Weight Watcher as a trademark name dates from 1960. To pull one's weight (1921) is from rowing. To throw (one's) weight around figuratively is by 1922. Weight-training is from 1945. Weight-lifting is from 1885; weight-lifter (human) from 1893.
Adjectival use wee bit apparently developed as parallel to such forms as a bit thing "a little thing." Wee hours "hours after midnight" is attested by 1891, from Scottish phrase wee sma' hours (1819); so called for their low numbers. Wee folk "faeries" is recorded from 1819. Weeny "tiny, small" is from 1790.
Proto-Indo-European root meaning "to go, move, transport in a vehicle."
The root wegh-, "to convey, especially by wheeled vehicle," is found in virtually every branch of Indo-European, including now Anatolian. The root, as well as other widely represented roots such as aks- and nobh-, attests to the presence of the wheel — and vehicles using it — at the time Proto-Indo-European was spoken. [Watkins, p. 96]
It forms all or part of: always; away; convection; convey; convex; convoy; deviate; devious; envoy; evection; earwig; foy; graywacke; impervious; invective; inveigh; invoice; Norway; obviate; obvious; ochlocracy; ogee; pervious; previous; provection; quadrivium; thalweg; trivia; trivial; trivium; vector; vehemence; vehement; vehicle; vex; via; viaduct; viatic; viaticum; vogue; voyage; wacke; wag; waggish; wagon; wain; wall-eyed; wave (n.); way; wee; weigh; weight; wey; wiggle.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit vahati "carries, conveys," vahitram, vahanam "vessel, ship;" Avestan vazaiti "he leads, draws;" Greek okhos "carriage, chariot;" Latin vehere "to carry, convey," vehiculum "carriage, chariot;" Old Church Slavonic vesti "to carry, convey," vozŭ "carriage, chariot;" Russian povozka "small sled;" Lithuanian vežu, vežti "to carry, convey," važis "a small sled;" Old Irish fecht "campaign, journey," fen "carriage, cart;" Welsh gwain "carriage, cart;" Old English wegan "to carry;" Old Norse vegr, Old High German weg "way;" Middle Dutch wagen "wagon."
mid-14c., ponderen, "to estimate the worth of, to appraise" (a sense now obsolete), from Old French ponderer "to weigh, poise" (14c., Modern French pondérer) and directly from Latin ponderare "ponder, consider, reflect," literally "to weigh," from pondus (genitive ponderis) "weight," from stem of pendere "to hang, cause to hang; weigh" (from PIE root *(s)pen- "to draw, stretch, spin"). Meaning "to judge (a matter or action) mentally, weigh carefully in the mind" is attested from late 14c. Related: Pondered; pondering; ponderation (1550s in the mental sense).
late 14c., poisen, "to have (a specified) weight," a sense now obsolete, from Old French poiser, stressed form of peser "to weigh, be heavy; weigh down, be a burden; worry, be a concern," from Vulgar Latin *pesare, from Latin pensare "to weigh carefully, weigh out, counter-balance," frequentative of pendere (past participle pensus) "to hang, cause to hang; weigh; pay" (from PIE root *(s)pen- "to draw, stretch, spin").
The meaning "to weigh, ascertain by weighing or balancing is from 1590s, hence the meaning "to hold or place in equilibrium or balance," from 1630s (compare equipoise). The intransitive sense of "be balanced or suspended," figuratively "to hang in suspense" is by 1847; the passive sense of "to be ready" (for or to do something) is by 1932. Related: Poised; poising. In 15c. a poiser was an official who weighed goods. The secondary sense of "to ponder, consider" in Latin pensare yielded pensive; that sense was occasional, but rare in Middle English poise.
1640s, "to be equivalent;" 1650s, "to counterbalance, make up for, give a substitute of equal value to," from Latin compensatus, past participle of compensare "to weigh one thing (against another)," thus, "to counterbalance," etymologically "to weigh together," from com "with, together" (see com-) + pensare, frequentative of pendere "to hang, cause to hang; weigh; pay" (from PIE root *(s)pen- "to draw, stretch, spin"). Meaning "to recompense, remunerate" is from 1814. The earlier verb in English was compense (late 14c.). Related: Compensated; compensating.